The grooves represent guides for the needles. During the needle travel stitch loops are formed by cooperation with the sinkers. The basic stitch forming process is described with reference to FIG. 1 which illustrates the prior art.
The cylinder is indicated by 1 and its groove by 2.
The number of grooves is equal to the number of needles 3. The needles reciprocatingly slide within the grooves.
Generally, the number of grooves and needles is between 200 and 400 per cylinder.
The needles operate with a reciprocating movement between a maximum position and a minimum position. They are moved by knitting cams, not shown.
The cylinder is rotated. The needles rotate with the cylinder and during their reciprocating movement the needles are fed with yarn when they reach their highest point of travel. This occurs when the needles are in a fixed angular position. When producing hosiery articles, generally only part of the available needles are used at the same time and in the same manner, with the exception of plain knitwork layers. In plain knitwork layers all the needles are operated between their maximum and minimum level, and all are fed with yarn at each knitting course, and all moved in the same manner.
When the machine is not producing plain knitwork, in order to produce other types of knitwork (such as mesh or patterned knitwork) some needles are required to produce stitch loops while others have to be raised to an intermediate level to take up yarn without clearing the previous stitch, to form a tuck stitch, or have to be raised with a certain delay so that they do not pick up the yarn fed into a certain angular position and therefore do not form new loops with it. In other words a needle selection has to be made. This means that for each revolution of the cylinder a certain number of needles must undergo a certain travel and a certain number of other needles must undergo a certain different travel or indeed undergo no travel.
This selection is made by the jacks 4 which slide in the same grooves as the needles lying above them, and which move these latter to a higher level in order to seize the yarn. When the jacks have moved the needle into its working position they withdraw from the needle butt and return downwards. If the needle, after completing its task of seizing the yarn and forming the stitch loop and therefore being at its minimum level, is not required to pick up a further yarn from another feed it remains at this level because its control jack remains in its lower rest position.
The jack 4 has a special shape which corresponds to a precise function. Although not shown on the drawing, it is slightly curved, or bowed, in a direction orthogonal to the plane of the drawing. This curvature keeps the jack lightly forced towards the inside of the groove and ensures its accurate positioning and lack of vibration by keeping it properly adhering to the walls of the groove and requires, the application of a force to move it either axially or radially.
The shank of the jack comprises a plurality of projections in its lower part.
The highest projection 5, namely the upper guide butt, comes into engagement with its own control cam 6 which again urges the jack downwards when it has completed its task of pushing the needle 3. Proceeding downwards along the jack shank there is a series of projections 7 known as teeth or pattern butts, which perform the actual selection described hereinafter and are provided in a number sufficient to provide the required number of selection combinations. At the foot of the jack there is the lower guide butt 8.
Said butt 8 cooperates with two fixed cams located about the base of the cylinder 1.
The cam 9 positions the butt 8 radially by urging it outwards so that it engages the cam 10, which moves the butt 8 vertically upwards.
All the jacks are urged outwards by the cam 9 so that they engage the cam 10, by which they are raised and urge their needle into its operating position.
The purpose of the selection mechanism and procedure is to exclude from this totality of jacks the jacks which control those needles which in order to form the desired knitwork have to be raised only to an intermediate level by means of the cam A to make a tuck stitch.
In the known art, the mechanism for selecting the needles, or more precisely for inactivating the jacks, consists of a plurality of members which come into contact with one of the butts 7 of the jack, and urge this jack back into the groove 2 so preventing it from making contact with the next lifting cam 10.
FIG. 1 shows schematically the movement involved in inactivating the jacks by means of levers 11 which rock about a horizontal pivot 12, in accordance with the prior art.
FIG. 1 shows by way of example two travel levers, of which a lever 11, pivoted at 12, is rotated into the inactivation position to interfere with that butt 7 located at its own level, thus urging it back into 2, whereas the lever 11', pivoted at 12', is rotated into its non-inactivation position so that it does not interfere with that butt 7 located at its own level, by virtue of being positioned within the gap between the two adjacent butts. The selection procedure therefore consists of producing contact between a certain number of levers 11 and a certain number of jacks 4 by way of pattern butts 7 located at the same height, by moving to their level only some of the levers 11. If a determined jack is to be left engaged with 10 while one or more of the levers 11 are to remain in the interference position, those butts corresponding to the height of these levers are removed from the jack. The number of levers available for selection control is generally equal to the number of pattern butts 7 available. The selection procedures of the known art generally consist of producing contact between the non-removed butts 7 of the jacks 4 and the inactivation members 11 by rotating said inactivation members into a position of non-interference with said butts. Obviously those levers 11 which are not required to inactivate the jacks whose butts 7 are in a corresponding position to them are kept in the non-interference position at the moment in which they would have made contact.
In circular knitting machines of high productivity the needle selection must be accomplished at high speed, as the selection speed governs the machine rotation speed and its productivity, and in addition the needle selector must occupy only a narrow angular space. In this respect, the angular sector occupied by the selector must be considered a "dead" space in which the jacks cannot move axially.
The angular width of said "dead" space is equal to the sum of the horizontal physical space occupied by the width of the lever 11, which must have a profile corresponding to gradual approach, and the space determined by the selector response time, which is given by the product of the speed of rotation of the machine cylinder and the time taken by the selector device to switch the lever 11 between its interference position and its non-interference position.
The angular width of said dead space could be reduced by reducing its two component terms.
To reduce the angular space physically occupied by the lever 11, they all can be positioned at the same angular coordinate in a stacked arrangement which is described hereinafter. This is to reduce the angular space determined by the selector response times. Selectors of very low inertia must be constructed and actuators of high switching speed used. With regard to reducing the physical space occupied by the selection member 11 it has been proposed in the known art to stack a number of selection members 11 of rocker lever type with their approach profiles all at the same angular coordinate. This number should be equal to the available number of butts 7, and to arrange the electromagnetic actuators in a position opposite them on the other side of the pivot 12 in adjacent stacks. The stacks should be staggered because of their vertical bulk, these occupying a larger vertical space than the members 11. The length of the pivot 12 must then be such that the opposite end of the lever 11 is also presented at the different angular coordinate at which its actuator has been disposed and must therefore be substantially as long as the width of the stack of staggered adjacent actuators.
In the embodiments described in French patent No. 1,564,603 in the name of Mayer & Cie and in British patent No. 1,436,607 in the name of Precision Fukuhara Works Co. Ltd., the vertical space occupied by each electromagnetic actuator is about three times the vertical pitch of the selection levers; the magnetic actuators are therefore disposed side by side in threes and staggered vertically, the pivot 12 being as long as three side-by-side actuators. The selection member 11 is always in the same position, but its opposite end is positioned to correspond to the position of the magnetic actuator which controls it.
In European patent application No. 219,029 in the name of Lonati S. p. A. the actuators are arranged in fives staggered side by side, the pivot correspondingly having the length of five side-by-side actuators.
The electromagnetic selection action can be exercised directly on the lever member 11 by attraction and/or repulsion action on its opposite end as in the case of the said Mayer and Fukuhara patents. It can also be exercised indirectly as in the case of the said Lonati patent and British patent application No. 2,008,157 in the name of Shima Idea Center Co. Ltd., in which the electromagnetic actuator consists of a lever rocking between two positions, determined by the excitation of two electromagnets facing it in opposite positions, this lever controlling the selection lever 11.
The devices of the known art suffer from considerable drawbacks in their practical application because the needle selection involves rather large forces and is very arduous.
In this respect, as the end of the selection lever 11 is shaped for progressive action, for each jack inactivation procedure the end of the lever 11 gradually receives the reaction R of the jack which is urged into the groove 2. This reaction can be as high as several hundred grams, especially when the thrust is exerted on the highest butts, and it can be repeated with high frequency of the order of hundreds of times per second.
The rocking masses must be reduced to a minimum otherwise the selection and switching speeds would be reduced because of their inertia.
The requirement for rapid switching from one position to the other is in conflict with the requirement of strength to resist the periodic impact against the butts 7.
In European patent application No. 279,310 in the name of Lonati S. p. A. the selection lever is again in elongated form so that it presents itself to a plurality of side-by-side electromagnetic actuators disposed at its rear, but is lightened by being constructed of synthetic material with lightening slots, the use of metal being limited to that end of the lever 11 which comes into contact with the butts.
This expedient reduces the inertia of the lever 11, but means that the reaction R, the impacts and any vibration must all be withstood by this synthetic material, which even if fibre-reinforced is much less resistant than the normal steel used for mechanical construction. The jack reaction R is in fact transferred between the metal part and the pivot 12 via the synthetic material.
The present invention provides a low inertia selector device of high resistance to the reaction forces exerted by the jacks.